[rubber_duck]

I'm against letting juniors or random devs introducing stuff you don't want to maintain in to your codebase for the sake of using the latest fad tech, chances are they will leave anyway and you will be left holding their mess. If they know what they are doing (ie. you hired someone with experience in stack Y and they want to help you migrate) then I'd say go for it if you can afford it. But picking a "safe but boring" stack puts you in the same hiring pool as everyone else picking that stack - can you compete on other terms to attract employees ?

Let's say you decided to write a webapp a few years back when RoR and AngularJS/CoffeScript was the popular stack. You wanted to write it in Clojure but you though "I can't hire Clojure devs reliably and RoR is popular so let's go with that". You are a small business/not high growth - you grow your app steadily - you now have a sizeable codebase on a legacy code stack that nobody really wants to touch or learn, there are plenty of job openings on that stack you have to compete with. Meanwhile people enthusiastic about Clojure were probably above average developers who would be happy to take below market rates just to work on a stack they enjoy and you could easily find people even today.

In a market where demand outpaces supply I'd say the "safe stack" is not a correct choice for small companies - if you have the know-how to pull off something more cutting edge. If you don't then ofc. use what you can to get the job done.